Dynamic characteristics and fragmentation evolution of columnar rockfall: A case study of the Zengziyan rockfall in Chongqing, China

Columnar rockfall occur widely in China and cause extreme damage to man-made structures and facilities. On 12 August 2004, Zengziyan W12 perilous rock collapsed and ran out a horizontal distance of 600 m. The rockfall caused airblast with a height of 150 m. In this paper, the dynamic characteristics and fragmentation evolution is studied based on the discrete element software MatDEM. The simulation of the rockfall process is achieved based on the discrete element model with real distribution of joints. The simulation is valid by comparing the simulation and video data. Through deeper development on MatDEM, the rock size evolution is analyzed, it was found that there were four significant breakage moments during the rockfall. The moments are rock compression breakage at the bottom of the rockfall, collision breakage of middle-upper rock mass with low-velocity triangle area, collision of middle and upper part of rock mass with ground, respectively. The fragmentation evolution of the pre- and post- rockfall is studied based on the fractal theory and dual parameters Weibull distribution. The results show that the proportion of fine particles increase obviously after the rockfall. This paper offers the basis of dynamic characteristics and fragmentation evolution of other rockfalls.